Toroidal electrodeless conductivity (EC) sensors are used to measure conductivity in a process fluid by use of electromagnetic cores, i.e., toroids. At least two toroids are typically used, one being a ‘drive’ toroid and the other being a ‘sense’ toroid. The sensor unit applies current to the drive toroid, which in turn induces a current in the sense toroid, through a current induced in the process fluid. The current induced in the sense toroid is proportional to the conductivity of the process fluid passing through the process pipe and through the toroids.
The toroidal conductivity sensors have been one of the industry standards for a long time. Until recently most of the toroidal sensors were invasive in nature, that is, the sensor protruded into the process flow. This has worked well in the industry for many years in many applications. However, in some applications the invasive nature of such toroidal EC sensors presents an undesirable impediment of the process flow. This impediment may be particularly problematic in applications in which the process flow is relatively thick and/or viscous, which tend to generate buildup around the sensor, which in turn, may lead to erroneous conductivity measurements.
Recently, flowthrough-type EC sensors have been developed to overcome the abovementioned problems associated with the use of invasive type toroidal conductivity sensors. An example of a sensor of this type is known as the 871FT™ toroidal electrodeless conductivity (EC) sensor available from Invensys Systems, Inc. (Foxboro, Mass.) in which the sensor portion is external to the process flow.
However, currently available industrial toroidal EC sensors are typically installed by hand-wiring the sensors either to an analyzer or junction box, e.g., using hand tools. A drawback of this approach is that this installation is relatively labor intensive, and there is a possibility that such hand-wiring may be performed incorrectly.
Moreover, in most industrial installations, the cable connecting the sensor to the analyzer or junction box is disposed within electrical conduit to prevent possible degradation of the cable either through weathering or exposure to many of the harsh chemicals used in the process industry. In many instances these sensors are located far away, sometimes at a distance of up to 30 m or more, from the analyzer. In these situations, if the sensor is to be removed for replacement, often some or all of the wiring needs to be removed and then reinstalled, causing undesirable delays and costs associated with process down-time.
These toroidal EC sensors also need to calibrated from time to time. For this purpose, toroidal EC sensors such as the aforementioned 871FT™ device, may be provided with calibration ports. These ports enable a user to input a specific known conductivity value to the sensor which may then be detected by the sensor in a conventional manner. However, in order to calibrate the process for low-end conductivity and/or to zero out the sensor, the process pipe typically needs to be drained completely of any process fluid. In an application in which the process pipe extends vertically, draining may be relatively easy to carry out. However, in an application with horizontal mounting, unless the process pipe is pitched, nominally the only way to accomplish the zero reading is to uninstall the unit and then thoroughly dry the inside of the process pipe. This may be relatively difficult and potentially hazardous, e.g., in the event the process fluid is caustic or otherwise aggressive. In either case, such emptying or drying of the process pipe of the process fluid poses a problem to the user because it generally requires that the process be shut-down, thereby increasing the cost of production.
Hence there is a need for a method of quickly replacing a sensor inline and for effecting low-end calibration of conductivity sensors without interrupting the production process.